1. The Field of the Invention
The present invention relates to methods and apparatus for administering substances to the eye. More particularly, the present invention discloses methods and apparatus for administering medicaments to the eye by iontophoresis.
2. The Relevant Technology
During ophthalmic medical procedures it is necessary to deliver a medicament to the eyeball, although the requirements for delivering medication to the eyeball vary depending on the particular medicinal purpose. For example, concentration levels of a medicament may be needed in the vitreous fluid of the interior of the eyeball to treat a particular affliction. However, for other pathological conditions, it may be efficacious to deliver and distribute medication over the entire surface of a sclera or to intra-sclera tissues. Yet another procedure may require an anesthetic compound to be carried or transmitted into the corneal tissue prior to a surgical procedure, such as keratotomy. Therefore, a given medical condition may require the delivery of a medicament over a widespread area, or conversely may need to be concentrated onto a smaller area.
One traditional method of delivering a medicament to the surface of the eye, either for treating a disorder or to aid in diagnosis, is through the use of eye drops. Generally, the lower eyelid is held away from the sclera and a drop of the medication is introduced into the gap formed between the eyelid and the sclera. During this procedure one must take care to avoid touching the eye with the dropper or one's fingers to reduce the risk of contamination. Through this procedure, numerous types of drug may be delivered to the eye, such as, antibiotics, corticosteroid, antihistamines. Additionally, eye drops may be used to administer drugs which control glaucoma and which either dilate or constrict the pupil. For example an ophthalmologist during an eye examination may drop tropicamide or phenylephrine onto the eye in order to dilate the pupil. By doing this the ophthalmologist will be able to fully view the crystalline lens and check for any defects. Furthermore, in cataract surgery, a physician may place a number of similar drops onto the surface of the eye in order to dilate the pupil so that most of the front surface of the lens is exposed. Additionally, a surgeon may use drops to introduce a local anesthetic instead of performing a local or general anesthetic with a needle.
Unfortunately, with the administration of medication through the use of an eyedropper there is the possibility of contamination, especially when multiple individuals use the same dropper. Furthermore, one may inadvertently contact the dropper with one's finger and thereby transmit any bacteria located on ones finger to the dropper. Additionally, medication may be required within the vitreous body of the eye, but the eyedropper only delivers medication to the surface of the eye and allows the medication to pass through the layers of the eye. The passage of medicament into the vitreous body may take a long period of time and hence reduce the effectiveness of eyedropper medicament delivery.
When a drug needs to be delivered below the surface of the eye, it is typical to utilize an injection. This is usually performed by inserting a needle into the tissue surrounding the eye or into the sclera of the eye. As a drug is injected into either region, it may be directed into the vitreous body or other surrounding tissue or other portions of the eye.
The use of a hypodermic needle, however, also has its disadvantages. Injection of a medicament is invasive, inconvenient and sometimes risky, due to the sharpness of the needle. As the physician inserts the needle into the surrounding tissues, a minor increase in the force applied may result in a perforated eyeball or a detached retina with the numerous associated problems. Additionally, many individuals are uneasy about the use of needles for any type of injection and more so when it involves inserting a needle close to or into the eye.
Another less common method used to administer a drug to an eye is known as iontophoresis. At the most basic level, iontophoresis involves the application of an electromotive force to drive ionic chemicals through a tissue so that they can be absorbed by adjacent tissues and blood vessels. In general terms, this is performed by placing a first bio-electrode containing an ionic medication solution in contact with a portion of the tissue which is to be phoresed. A second bio-electrode is placed on a part of the body near to the first bio-electrode, and a voltage is applied sufficient to cause current to pass through the tissue thereby completing the electrical circuit between the electrodes. As current flows, the ionized medication molecules migrate through the tissue under the influence of the second bio-electrode.
A similar approach is taken with respect to ocular iontophoresis, Traditionally ocular iontophoretic apparatus comes in one of two types, either an eyecup device or an applicator probe. The traditional eyecup device is formed from a half-spherical element. Normally the interior of the element is hollow and an electrode extends from the top of the half-spherical element. During iontophoresis, the eyecup is filled with a medicament solution and placed on the eye. As the voltage from a power source is applied, current passes from the electrode within the half-spherical element and flows into the surface of the eye. Simultaneously, the medicament ions are forced either from the cathodic bio-electrode within the half-spherical element towards the anodic bio-electrode, or vice versa, thereby forcing the medicament into the eye of the patient.
In an alternative ocular iontophoretic device, an applicator probe may be used. An applicator probe has an electrode which extends into a probe end that is filled with a medicament. The probe end is placed on the patient's afflicted area and medicament migrates from the probe end into the patient's tissue as current is applied.
Conventional ocular iontophoretic apparatus have a number of problems. For example, an applicator probe device requires one to precisely and continuously hold the probe against the patient's eyeball. Unfortunately, if the entire eyeball has to be phoresed this procedure can take a long period of time. Additionally, if one applies too great a force, too high a current, or maintains contact for too long a period of time, the patient's eyeball can be burned leaving lesions on the eye surface. Furthermore, with the eyecup-type apparatus, there is a possibility that one may scratch the eyeball of the patient if the probe is too long or if placement is not accurate. Also medication which is placed within the eyecup may escape from beneath the edges of the eyecup due to conformability limitations of the eyecup and variations in the size and curvature of the eyeball, Additionally, contaminants, such as tears, saline, or other impurities may infiltrate the medicament thereby reducing the potency or pharmacological effectiveness of the medicament. The eyecup may be forced against the surface of the eye to reduce the effects of leaking and containment infiltration, however, the required force may damage the eye.
Perhaps the most significant problem with prior ocular iontophoretic devices is the unintentional delivery of medicament to the surrounding soft tissues, including the eyelid, socket, etc, instead of to the eyeball or sclera. This inadvertent drug delivery to the surrounding tissues is due to the sclera and other eyeball tissues being wetted with conductive saline or tears. The saline or tears has considerably lower electrical resistance than alternative transscleral pathways, resulting in the electrical current preferentially following a pathway to the surrounding soft tissues.
It would be an advantage, therefore, to provide an apparatus which may be used to administer medicaments to any region of an eyeball, while preventing inaccurate distribution of medicament to surrounding tissues and damage to the eye.